Many products may be perishable, since they degrade over time becoming less suitable for their intended use; generally, the perishable products should be used before corresponding expiration dates at which they are expected to become substantially unsuitable for use (for example, because they are of poor quality, ineffective, unsafe, dangerous). Typical perishable products are drugs. Indeed, the drugs may lose strength, may increase concentration of active ingredients, may develop harmful substances, may be contaminated over time; therefore, the drugs may cause missing treatments, overdoses, intoxications, illnesses if taken after their expiration dates (thereby causing more or less serious damages to their users).
In view of the above, most of the perishable products have their expiration dates that are printed on corresponding packages (for example, boxes). However, the expiration dates may be difficult to read (especially for old people) and they may be lost (for example, if the packages are damaged or binned).
In any case, the expiration dates that are provided on the packages are nominal values defined under the assumption that the perishable products have been maintained under prescribed conditions. However, many events may (adversely) affect the expiration dates of the perishable products. For example, the perishable products may have effective values of the expiration dates that are significantly shorter than their nominal values when the perishable products have undergone prolonged exposures to high temperatures, illuminations; moreover, most perishable products should be used within a short time once their packages have been opened. As a result, the nominal values of the expiration dates are set conservatively; however, this causes the discarding of many perishable products that instead are still suitable for use. In any case, it is very difficult (if not impossible) for the users of the perishable products to recognize the effective values of the expiration dates of the perishable products; this may cause the usage of perishable products that are of poor quality, ineffective, unsafe or dangerous (with all the above-mentioned risks for their users).